This invention relates to biodegradable expanded or foamed starch products including packaging products having low bulk density and low dustiness properties and further to the method of preparing such products.
Starch, a readily available biodegradable material has been used to prepare foamed, film and other shaped products for different purposes. Some of these starch products and their uses are described in U.S. Pat. Nos. 5,035,930 and 5,043,196 both issued to N. Lacourse et al on Jul. 30, 1991 and Aug. 27, 1991 respectively, showing the extrusion of starch having high amylose content of at least 45% by weight into expanded packaging products. U.S. Pat. No. 5,095,054 issued to G. Lay et al on Mar. 10, 1992 discloses thermoplastic polymer compositions comprising destructurized starch with a variety of thermoplastic polymer materials. These compositions include modified and unmodified starches with polymers such as polyolefins, vinyl polymers, polyacetals, polyesters, polycarbonates, polyethers, etc. The patent further discloses processes for forming such compositions into shaped articles.
In recent years, because of its ready availability and environmentally friendly characteristics, numerous attempts such as those described above, have been made to form starch and its derivatives into different products. Other disclosures include U.S. Pat. No. 5,393,804 issued Feb. 28, 1995 to E. George et al which shows the formation of articles using biodegradable compositions comprising converted or degraded starch of low molecular weight, a plasticizer and alkenol polymers. Another disclosure, EP 0 712 883 published May 22, 1996, reveals the formation of shaped products using starch having a particular particle size. While these methods offer suitable properties for the particular type products they are disclosed for, they generally have not been suitable for applications where the combination of low bulk density as well as good flexibility or low embrittlement is required. This usually occurs where low bulk density starch products are being prepared because such products generally become more brittle as bulk density is reduced. This is especially true in providing products for packaging applications such as loosefill where products with very low bulk density and good flexibililty or low embrittlement are needed, particularly at low relative humidity when the problem is most pronounced.